<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <ul>
        <li>11111</li>
        <li>22222</li>
        <li>33333</li>
        <li>44444</li>
        <li>55555</li>
    </ul>
    <script src="jquery-1.12.2.min.js"></script>
    <script>
//        $("ul li:nth-child(odd)").css("backgroundColor", "blue");
        $("ul li").click(function(){
            $(this).css("backgroundColor", "red");
        })
    </script>
</body>
</html>